This disclosure relates generally to inorganic fibre mats. More specifically, although not exclusively, this disclosure relates to inorganic fibre mats and uses for the same.
Fibrous materials are well known for their use as thermal and/or acoustic insulating materials and are also known for their use as strengthening constituents in composite materials such as, for example, fibre reinforced cements, fibre reinforced plastics, and as a component of metal matrix composites. Such fibres may be used in support structures for catalyst bodies in pollution control devices such as automotive exhaust system catalytic converters and diesel particulate filters. Such fibres may be used as a constituent of friction materials, e.g. for automotive brakes. The fibres of the present disclosure have a range of properties and may be usable in any or all of these applications depending on the properties shown.
Prior to 1987 there were four principle types of fibrous materials used for making thermal insulation products (such as, for example, blanket, vacuum formed shapes, and mastics). These were made by two principal manufacturing routes, although the details of the particular routes vary according to manufacturer. The fibres and routes were (in order of increasing cost and temperature performance):
Melt formed fibres:                Mineral wools;        Glass wools;        Aluminosilicate fibres.        
Sol-gel process fibres:                So-called polycrystalline fibres.        
Melt formed fibres are formed by making a melt and fiberising the resultant melt by any one of the many known methods. These methods include:                forming a stream of melt and allowing the stream to contact spinning wheels from which it is flung to form fibres;        forming a stream of melt and allowing the stream to impinge upon a jet of gas that may be transverse, parallel with, or at an angle to the direction of the stream and thereby blasting the melt into fibres;        forming a fibre from the melt by a rotary process in which the melt escapes through apertures in the circumference of a spinning cup and is blasted by hot gases to form fibres;        extruding the melt through fine apertures to form filaments, and in which further treatment may be used (e.g. flame attenuation in which the filament is passed through a flame);        or any other method by which a melt is converted into a fibre.        
Because of the history of asbestos fibres, a lot of attention has been paid to the relative potency of a wide range of fibre types as a cause of lung disease. Studies of the toxicology of natural and man-made fibres led to the idea that it was the persistence of fibres in the lung that caused problems. Accordingly, the view developed that if fibres can be removed from the lung quickly, then any risk to health would be minimised. The concepts of “biopersistent fibres” and “biopersistence” arose—fibres that last for a long time in the animal body are considered biopersistent and the relative time that fibres remain in the animal body is known as biopersistence. Whilst several glass systems were known to be soluble in lung fluids, resulting in low biopersistence, there was a problem in that such glass systems were generally not useful for high temperature applications. A market need was seen for a fibre that could have a low biopersistence combined with a high temperature capability. In 1987 Johns Manville developed such a system based on a calcium magnesium silicate chemistry. Such material not only had a higher temperature capability than traditional glass wools, but also had a higher solubility in body fluids than the aluminosilicate fibres mostly used for high temperature insulation. Such low biopersistent fibres have been developed since, and a range of alkaline earth silicate [AES] fibres are now on the market. These alkaline earth silicate fibres contain low quantities of alumina, as alumina decreases the solubility of such fibres.
U.S. Pat. No. 8,088,701 claims potassium aluminosilicate fibres covering a broad range of compositions (Al2O3≥5 mol %; K2O 12-40 mol %; and SiO2 5-80 mol %) and corresponding properties. This document teaches the following: (i) to obtain fine fibres (<10 μm diameter), the silica content should be less than 40 wt. % or viscosity modifiers need to be added; (ii) to obtain the best high temperature performance a 1:1 molar ratio of K2O:Al2O3 is recommended; (iii) to obtain high temperature mechanical resilience, heat treatment of the fibres is recommended. Although the disclosed compositions have improved overall performance in comparison to conventional low biopersistent fibres, there still remains a need to improve performance, particularly at high temperatures.